Generally, glass materials are hard and also can be used in the form of films that coat substrates. However, when employing a melting method, a high temperature treatment is necessary to obtain a glass film (silica-based film). This limits the material of which the substrates and coating films can be made.
The sol-gel process is a process of obtaining an oxide in a solid state by: using a solution of an organic or inorganic compound of metal as a starting material; rendering the solution into a sol in which fine particles of metal oxides or hydroxides have dissolved through the hydrolysis reaction and condensation polymerization reaction of the compound contained in the solution; further gelling and solidifying the sol; and heating this gel.
The sol-gel process allows silica-based films to be produced at lower temperatures. However, the silica-based films obtained by the sol-gel process have a problem of being inferior in mechanical strength, particularly the abrasion resistance of a film, compared to silica-based films obtained by the melting method. Recently, the inventors found that, by improving the sol-gel process, a silica-based film with excellent abrasion resistance can be formed, while containing an organic material, and suggested an article provided with this silica-based film (organic-inorganic composite film) in WO2005/095101A1. This silica-based film has excellent abrasion resistance comparable to a glass sheet obtained by the melting method in the Taber abrasion test.
This improved sol-gel process uses a coating solution with its pH adjusted to about 2 including more water than the theoretical amount, and further including added hydrophilic polymer represented by a polyether surfactant. This process allows a film of over 250 nm thickness with excellent abrasion resistance to be obtained, without heat treatment at high temperatures (e.g. over 400° C.). In this process, the hydrophilic polymer remains in the formed film while serving to prevent excess contraction of the film that can accompany the evaporation of fluid components of the coating solution.
Formation of organic-inorganic composite films by the sol-gel process is disclosed in JP11(1999)-140310A and also JP11(1999)-140311A, for example.
In JP11-140310A, “an organic-inorganic polymer hybrid where a sol-gel reaction of tetraalkoxysilane is carried out in the presence of amphipathic poly oxazoline block copolymer (7) containing a hydrophilic segment of poly(2-methyl oxazoline) and a hydrophobic segment of poly(2-phenyl oxazoline), and a block copolymer (7) is uniformly dispersed in a silica gel matrix” is suggested.
In JP11-140311A, “an organic-inorganic polymer hybrid where a non-reactive polymer having amide bond, urethane bond and/or urea bond, and a hydrophobic low molecular weight compound, being at least one selected from the group consisting of a condensation aromatic compound and an anthraquinone compound, are uniformly dispersed in a matrix of a metal oxide” is suggested.